The invention relates to plasters, particularly epicutaneous test plasters with at least one active substance receiving or absorbing device located on a carrier film as well as to a process for the production thereof and to the use thereof.
Epicutaneous plasters are used in epicutaneous tests, which are used in particular for clarifying the causes of allergic contact dermatitis. For this purpose the test substance to be tested is applied to a test plaster, which is then applied to appropriate points of the patient's skin. The test plaster is then removed after a predetermined time.
The first reading or observation of the patient's reaction to the active substance exposure takes place immediately following test plaster removal and then further readings or observations occur at given intervals of time. It is helpful to be able to mark the test points on the skin, so that it is possible to reliably find again the skin point contacted with the test substance.
In principle, epicutaneous test plasters have the following structure. On a contact adhesive carrier layer are arranged active substance-absorbing devices in the form of absorptive textiles, e.g. of woven or non-woven fabric, or containers open towards the skin, or are formed in said carrier layer being able to absorb or take up the test substances. The test plaster surface to be contacted with the skin is covered with a removable protective layer prior to application. Hitherto flat textile materials, such as e.g. woven and non-woven fabrics, polymer or metal films and foils have been proposed as the carrier layer. The disadvantage of these materials is that the carrier materials have an inadequate elasticity to completely prevent the premature detachment of the test plaster from the skin through unavoidable body movements and avoid the irritations caused by rubbing on the active substance absorbing devices, which can simulate an allergic reaction.
It is also desired, particularly in the case of Plasters which remain a long time on the skin, that they are on the one hand watertight, so that they are not damaged when the patient is washing or taking a shower, while on the other hand a permeability for water vapor is desired, in order to prevent maceration of the underlying skin layer. It has not been possible to realize this up to now.
The problem of the present invention is therefore to provide a plaster, particularly an epicutaneous plaster, which avoids the aforementioned deficiencies of the known solution proposals.
Surprisingly the problem has been solved in that the carrier film is made from a highly elastic polymer material, which is tight for liquid water, but permeable for water vapor and is detachably connected in whole-area manner or in partial surface portions on the surface remote from the skin to at least one support or backing film covering the surface of the carrier film.
In order to fulfil the requirements regarding a carrier material of an epicutaneous test plaster with respect to elasticity, watertightness and water vapor permeability, one possibility is to reduce the thickness of the polymer film, but the use of extremely thin films with these desired characteristics for such plaster types has failed up to now due to the difficulty of handling said films. They have a very limited flexural rigidity, being so-to-speak flabby, crease very easily and therefore tend to adhere to themselves on application. In order to permit the use of such films for plasters, particularly epicutaneous test plasters, the invention makes use of a surface stabilization, in which the extremely thin film is reinforced by joining to a thicker, more rigid, second film until application has taken place. This surface-stabilizing film is referred to as the support film and has at least the size of the film to be stabilized. Advantageously it is allowed to project over the film to be stabilized on at least one side, so as to provide a gripping or handling edge for the subsequent removal of the support film.
According to another preferred realization of the invention the support film projects so far over the edge of the carrier film that, parallel to said edge, is offered space for a contact adhesive marking strip separated from the carrier film and which on application of the active substance absorbing device it adheres alongside the same to the skin and, following the removal of the plaster, preferably remains on the skin and is available for marking the test point.
Said marking strip can e.g. be colored. The epicutaneous test plasters according to the invention can be in the form of individual plasters, i.e. with only a single active substance absorbing device, but preferably have several active substance absorbing devices arranged in accordance with a predetermined geometrical pattern and preferably in rows. Between the individual active substance absorbing devices can be provided predetermined breaking lines, which permit an easy separation of a plaster with the desired number of active substance absorbing devices from a longer plaster web.
The carrier film which is impermeable to liquid water and permeable to water vapor to be used according to the invention has a suitable polymer, examples of which are polyurethanes, polyvinylchlorides, polyvinylidene chlorides, polyvinyl alcohols, polypropylene, polyamides, ethylene-vinylacetate copolymers, polyesters, polycarbonates, polyvinylfluoride and other fluorine-containing polymers. Polyurethane-based carrier films are particularly preferred. The layer thicknesses of suitable carrier films are in the range 5 to 120 pm, preferably 10 to 50 .mu.m. Their water vapor permeability should be at least 300 g/m.sup.2 /24 hours.
The one or multi-layer support film preferably contains suitable polymers, or also metals. Suitable polymers are e.g. polyethylene, polypropylene, polyamides and polyesters. Optionally said films are siliconized on the skin side, in order to obtain the necessary separating force between the carrier film and the support film. The film thickness can be 20 to 200 pm, preferably 30 to 80 pm. The gripping edge optionally formed on the support film must be sufficiently wide to ensure easy handling. Preferably the support film is not detachably connected to the carrier film by adhesion and instead the connection is brought about by mechanical coherence, which is e.g. obtained if the carrier film is produced directly on the support film by extrusion, molding or some other film production procedure. In the case of coextrusion of both films it must be conversely ensured that the two films can be separated from one another. The skin side of the carrier film is covered with a contact adhesive layer for which purpose the known physiologically unobjectionable contact adhesive materials are suitable. Examples are rubber, rubber-like synthetic homopolymers, copolymers and block polymers, polyacrylates and their copolymers, polyurethanes and silicones. The surface application of the contact adhesive is between 15 and 80 g/m.sup.2, preferably between 30 and 50 g/m.sup.2.
The active substance absorbing devices are preferably portions, such as circular disks or other surface shapes of absorptive material, such as e.g. paper, woven and non-woven fabrics and gel-like polymers, which can supply the active substance to the skin or comprise a small shell or dish for receiving the active substance, such as a test substance. They are fixed in per se known manner to the contact adhesive layer. In order to prevent an unintentional migration of the liquid active substance or active substance formulation from the active substance absorbing or receiving devices, the latter can be covered with a film ring dimensioned in such a way that with half its width it covers the active substance absorbing device and with the other half is fixed to the contact adhesive layer, without impairing the skin contact surface of the active substance absorbing device.
The plaster is preferably covered on the contact adhesive side by a protective layer prior to application. This protective layer can be in one or more parts and adjacent parts can overlap in order to form a gripping aid for removing the protective layer. In principle, all materials suitable for the support film can be used for the optionally multicoat protective layer. However, it is also possible to use in exemplified manner polytetrafluoroethylene, cellophane, polyvinylchloride, treated papers, metal foils and polymer-coated metal foils. The substance weight is 50 to 200 g/m.sup.2, preferably 80 to 150 g/m.sup. 2. The protective layer side in contact with the contact adhesive layer must permit a removal of the protective layer from the remainder of the plaster with a force smaller than that required for removing the support film from the carrier film.